The presence of blood in feces can signal the existence of a tumor, ulcer, or other medical disorder along the digestive tract. In early stages of development, a tumor or ulcer on the digestive tract may bleed to such a slight extent that the blood, while present in the feces, is not visible. Nonetheless, in such cases, the blood, termed "hidden" or "occult" blood, can usually be detected with one of a number of indicator reagents which change color in the presence of the hemoglobin in blood.
One of the most widely used occult-blood indicator reagents is derived from an extract from the wood of certain species of trees of the Guaiacum genus native to the American tropics. The extract, termed guaiac, turns from essentially colorless to blue in the presence of hemoglobin and an oxidizing agent such as hydrogen peroxide. More specifically, the guaiac reagent is sensitive to what is termed "peroxidase activity" which results from the combination of an oxidizing agent with hemoglobin or certain chemically similar compounds.
Testing feces for the presence of occult blood with an occult-blood indicator reagent is a valuable medical diagnostic tool, since such testing can often detect tumors in the digestive tract at an early stage of their development, typically before the tumors manifest other symptoms and at a stage when they can be treated most successfully.
A procedure widely used by physicians and medical laboratories for testing for occult blood in fecal matter makes use of a test slide of the type disclosed in U.S. Pat. No. 4,365,970 to Lawrence and Townsley. The test slide of the Lawrence and Townsley patent includes a sheet of guaiac-impregnated indicator paper enclosed in a cardboard envelope. A front panel of the envelope has openings in it for smearing samples of fecal matter on a first side of the indicator paper. A rear panel of the envelope has an opening for applying a hydrogen peroxide developing solution to a second side of the indicator paper. A blue stain on the indicator paper signifies the presence of occult blood in the sample of fecal matter on the opposite side. Since the blue stain appears on the side of the indicator paper opposite to the samples of fecal matter, the developing solution necessarily soaks through the paper in the test procedure. The indicator sheet of the test slide of the Lawrence and Townsley patent has a control area designated on its second side which includes a positive monitor and a negative monitor. Hemin, a hemoglobin-derived compound, is printed on the positive monitor, but not on the negative monitor. Application of the developing solution to the control area causes the indicator paper to turn blue at the positive monitor and remain colorless at the negative monitor if the test reagents are properly active and if the test slide has not been contaminated with a compound which yields a false indication of the presence of hemoglobin.
Although the test slide of the Lawrence and Townsley patent is generally satisfactory for use in a doctor's office or a hospital, it has significant disadvantages for home use. An applicator stick must be used to collect each sample of fecal matter from a toilet bowl and to smear the sample on the test slide. The person using the test slide thus has the problem of disposing of the applicator sticks and, after applying the developing solution to the slide, disposing of the test slide itself. Neither the applicator sticks nor the test slide can be flushed down the toilet. Even if the test slide is forwarded to a doctor's office or medical laboratory for analysis, the problem of disposing of the soiled applicator sticks remains for the user.
U.S. Pat. No. 4,175,923 to Friend discloses a test for the presence of occult blood in fecal matter which is intended to be carried out at home. The test makes use of an indicator paper prepared by impregnating a sheet of absorbent paper with guaiac reagent. A portion of the indicator paper is also impregnated with blood. The test of the Friend patent involves applying a developing solution to a sheet of the indicator paper and then tossing the sheet into a toilet bowl to contact the paper with the water in the bowl. The developing solution causes the portion of the indicator paper impregnated with blood to turn blue if the guaiac reagent and developing solution are properly active. If stools in the toilet bowl contain occult blood, blood will disperse in the water in the bowl. Blood in the water in the toilet bowl will in turn cause the remainder of the indicator paper to turn blue. After allowing time for the color of the indicator paper to change, the paper can be flushed down the toilet with the stools.
Although the occult-blood detection test of the Friend patent is satisfactory in principle, it is limited in a number of respects. Ordinarily, for occult blood in fecal matter to be detected by the test, the blood must disperse in the water of the toilet bowl. Such dispersal necessarily dilutes the blood and thus reduces the sensitivity of the test. In addition, the test results may be suspect as a consequence of the presence of contaminants in the toilet bowl. Furthermore, guaiac reagent is subject to degradation by oxygen in the air. Consequently, the sheets of indicator paper are preferably stored individually in sealed foil envelopes or air-tight packages of some other sort to increase shelf-life stability. Such air-tight packaging increases the cost of the test to the user.